1. Field of the Invention
This invention relates generally to a seedling detector and more specifically to an optical seedling detector mounted on the teeth of a comb between which teeth pass the seedlings.
2. Description of the Prior Art
A major agricultural business has developed around the growth of seedlings from seeds for transplanting purposes. The plants may be almost any species, but of special importance are vegetable and tree seedlings. Such seedlings are grown in greenhouses and when of a suitable transplant size are, shipped out for planting on farms or timberland. To facilitate handling, the seeds are placed in a small container having a suitable growth material with a large number, for example 200, of the containers being held by a tray. The tray may have a two dimensional grid of cells for holding the containers, for example 200 cells may be arranged in a pattern of 10 rows by 20 columns.
In order not to waste space in the greenhouse, it is economically important to have a seedling growing in each container. In the past, this was accomplished by planting two or more seeds together, thus increasing the probability that at least one would emerge per container. Unfortunately, this is a waste of seed and also requires surplus step of plucking out the extra seedlings. In addition, some containers would still have no seedling. Some devices, such as the one shown in U.S. Pat. No. 3,852,914, have been developed to test seeds before planting to get a better percentage of plants emerging. However, these attempts have not been completely successful.
Another method of avoiding the problem is to plant a single seed per container, and at a point in time after the plants have emerged, but before they are large enough for transplanting, to sort out those containers without emerged seedlings. The empty cells left in the tray may then be filled with containers having emerged seedlings so that every cell in the tray has a seedling. This procedure although technically successful, has been performed by hand and as a result has been time consuming and expensive.
Attempts at using machinery to perform this task have been only partially successful. While conveyor equipment for moving the trays and may be obtained by modification of existing equipment, the determination of the presence of a seedling has been difficult. This is especially true as the efficiency and speed of the other equipment increases, thus causing a bottleneck at this point in the assembly line.
Automatic detecting devices, especially optical detectors are well known for the detection and inspection of various items. However these items are much less fragile than young seedling plants and do not occur in a grid such as the tray of plants. U.S. Pat. No. 4,266,674 shows a light and photodetector arrangement for a pack of cigarettes which determines when a missing cigarette leaves a hole. U.S. Pat. No. 4,408,295 shows another arrangement of detectors to find an empty hole indicating a missing item. Since seedling trays hold the container even if the plant has not grown, these devices are not usable for such application. U.S. Pat. No. 4,166,948 shows a detector in each chute of a planter dispensing seed corn. However, this requires the item to fall through a chute which cannot be done with a tender seedling.